The present invention relates to a laser beam controller used in a digital copying machine etc.
In a digital copying machine using a laser beam for creating a latent image, the place where a laser beam is irradiated makes a black point and the place where a laser beam is not irradiated makes a white point in a copied image. When the laser beam control is such that the whole area of a unit pixel is either fully irradiated (black) or not irradiated (white), the gradation appearance of the copied image is poor. One method of increasing the gradation of the copied image is to reduce a spot size of the laser beam and thereby the spot of the beam is irradiated onto a limited portion (or portions) of a pixel area. Another method is to vary the duration of the laser beam irradiation time while maintaining a predetermined size of a spot of the laser beam. In the latter method, the width of a clock pulse for generating a laser beam may be varied to multi-widths (e.g., four widths).
In the former method where a laser beam size is controlled, however, some analog processings must be introduced in the laser beam control circuit, which complicates the control circuit and the design. In the latter method, the clock pulse should be very small (i.e., the clock pulse should have very high frequency). Accordingly, the latter method requires a very high frequency circuit to generate the clock pulse, which is generally expensive.